Electroluminescent device

ABSTRACT

The invention relates to an electroluminescent device ( 10 ) comprising a layer system with a substrate ( 40 ) and on top of the substrate ( 40 ) a substrate electrode ( 20 ), a counter electrode ( 30 ) and an electroluminescent layer stack with at least one organic electroluminescent layer ( 50 ) arranged between the substrate electrode ( 20 ) and the counter electrode ( 30 ), characterized in that at least one optical transparent outcoupling body ( 71 ) is provided on top of the substrate electrode ( 20 ) to increase the outcoupling of light generated by the at least one organic electroluminescent layer ( 50 ) at least partly covering the optical transparent outcoupling body ( 71 ). The invention further relates to a method to manufacture such a device.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application a continuation of U.S. patent application Ser. No.13/319,110, filed on Nov. 7, 2011, which is U.S. National Phaseapplication under 35 U.S.C. §371 of International Application No.PCT/IB2010/051896, filed on Apr. 30, 2010, which claims the benefit ofEP Patent Application No. EP 09159731.0, filed on May 8, 2009. Theseapplications are hereby incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to an electroluminescent device comprisinga layer system with a substrate and on top of the substrate a substrateelectrode, a counter electrode and an electroluminescent layer stackwith at least one organic electroluminescent layer arranged between thesubstrate electrode and the counter electrode with increased outcouplingof light. Furthermore, the invention relates to a method formanufacturing an electroluminescent device with an increased outcouplingof light.

BACKGROUND OF THE INVENTION

A typical organic light emitting device (OLED) comprises a glasssubstrate, a transparent substrate electrode, e.g. Indium-Tin-Oxide(ITO), an electroluminescent layer stack and a reflective counterelectrode. Light generated from the device is emitted through the glasssubstrate. The indices of refraction of the substrate electrode, theelectroluminescent layer stack and of glass are typically 1.9 to 2.0,1.7 to 1.9, and about 1.5, respectively.

Due to the differences between the refractive indices of the substrate,the layers and the environment, usually air, most of the light generatedin the OLED is not able to escape from the substrate to the outside.Typically, the generated light is divided into the following fractions:30% of the light is trapped in the light guide formed by the organiclayers and the ITO, about 20% is lost in the interaction with themetal-cathode, about 50% enters the glass substrate and from the glasssubstrate only 20% can escape to the outside. According to the priorart, different means for an improved light outcoupling are alreadyknown, e.g. layers with light scattering properties, but unfortunatelyleading to different disadvantages.

As an example, EP 1 734 792 A1 discloses an electroluminescent devicecomprising a reflective electrode with light-scattering andlight-reflecting properties. Unfortunately, said structuring of thesubstrate electrode is limited within the nm-range and is limited toonly a low improvement of said light outcoupling.

EP 1 763 081 A2 discloses an OLED with a substrate featuring a number ofrecesses, in which a non-transparent reflective material is buried in,in order to reflect light captured within the substrate to the substratesurface with another propagation direction to couple out the light tothe environment. Unfortunately, the manufacturing of a substratecomprising recesses in order to embed in said non-transparent reflectivematerial is complex and costly. Moreover, the amount of emitted light,captured within the layers on top of the substrate will not be coupledout with this measure.

SUMMARY OF THE INVENTION

Thus, the invention has for its object to eliminate the disadvantagesmentioned above. In particular, it is an object of the invention todisclose an electroluminescent device with an improved outcoupling oflight. Moreover it is an object of the invention to disclose asimplified arrangement of light outcoupling means.

This object is achieved by an electroluminescent device comprising alayer system with a substrate and on top of the substrate a substrateelectrode, a counter electrode and an electroluminescent layer stackwith at least one organic electroluminescent layer arranged between thesubstrate electrode and the counter electrode, wherein at least oneoptical transparent outcoupling body is provided on top of the substrateelectrode to increase the outcoupling of light generated by the organicelectroluminescent layer at least partly covering the opticaltransparent outcoupling body. The object is also achieved by a methodfor manufacturing the electroluminescent device according to the presentinvention. Preferred embodiments of the electroluminescent device andthe method are defined in the subclaims. Features and details describedwith respect to the electroluminescent device also apply to the methodand vice versa.

The present invention discloses at least one optical transparentoutcoupling body provided on top of the substrate electrode to increasethe outcoupling of light generated by the at least one organicelectroluminescent layer at least partly covering the opticaltransparent outcoupling body. The optical transparent outcoupling bodymay be attached to the substrate electrode via thin adhesive means suchas glue not disturbing the optical properties of the outcoupling bodyand the substrate electrode. The optical transparent body may be amacroscopic rigid body. The optical transparent body may be preformedbefore applying the body to the substrate electrode comprising atransparent material, e.g. glass or plastic.

The leading idea of the present invention is to use at least one opticaltransparent outcoupling body, which is provided on top of the substrateelectrode. Thus, the optical outcoupling body is arranged between thesubstrate electrode and the electroluminescent layer stack comprisingsaid at least one organic electroluminescent layer. This arrangementallows the simply use of ITO-coated substrates, whereas the ITO-coatingforms the substrate electrode, deposited on a substrate forming thecarrier material. Said ITO-coated substrates are provided as standardsubstrates for electroluminescent devices, and are indicated by a highavailability and low costs.

Subsequently, the electroluminescent layer stack comprising at least oneorganic electroluminescent layer and said counter electrode is appliedon the optical transparent outcoupling body or on the outcoupling bodiesand also on the part of the substrate electrode surface, which is notcovered with said optical transparent outcoupling bodies.

When a voltage is applied between the substrate electrode and thecounter electrode, current is injected from the electrodes and saidelectroluminescent layer stack is excited to emit light in the area,where the electroluminescent layer stack is directly deposited on thesurface of the substrate electrode. As a result, the optical transparentoutcoupling body forms an isolation body, preventing a current injectionin the electroluminescent layer stack.

Combined with the advantage of an easy application of the at least oneoptical transparent outcoupling body, the emergence of a localenhancement of the electrical field in the area of sharp edges of thearranged optical transparent outcoupling body is avoided. Due to thenon-conductive behavior of said optical transparent outcoupling body,the local enhancement of the electrical field is avoided, when a voltageis applied between the substrate electrode and the counter electrode.

In one embodiment the optical transparent outcoupling body features ahigh index of refraction and preferably at least matching the index ofrefraction of the substrate in order to avoid a reflective indextransition between the optical transparent outcoupling body and thesubstrate leading to outcoupling losses. Typical values for therefractive indices of the glass substrate are 1.51 to 1.54, for thesubstrate electrode 1.9 to 2.0 and for the outcoupling body 1.5 to 1.6.

According to another preferred embodiment of the present invention, theoptical transparent outcoupling body is glued on top of the substrateelectrode. By the use of glue for applying said optical transparentoutcoupling body on top of the substrate electrode, a simple and easymanufacturing process is provided by using glue.

Yet another embodiment of the present invention provides glue forarranging said optical transparent outcoupling body on top of thesubstrate electrode, which features a high optical transparency. Thus,the glue for gluing the optical transparent outcoupling body on top ofthe substrate electrode forms optical transparent glue, featuring a highindex of refraction, whereas said index of refraction is at least equalto the index of refraction of the substrate material, but equal to orless than the refractive index of the optical transparent outcouplingbody. Thus, the optical transition between the optical transparent glueand the optical transparent outcoupling body is optimized and the lightin the substrate material can pass into the optical transparentoutcoupling body via the optical transparent glue.

There are two embodiments concerning the surface of the outcouplingbodies facing towards the counter electrode: In one embodiment, thesurface is transparent, such that light entering from the substrateelectrode side into the outcoupling body can exit towards the counterelectrode, where the light is reflected. In this embodiment, the lighthas to pass twice trough the organic electroluminescent layer stack infront of the counter electrode. In this case, the reflectivity isdetermined by the absorption in the organic layers and the counterelectrode.

In another embodiment the surface of the optical transparent outcouplingbody facing towards the electroluminescent layer stack and/or thecounter electrode is covered with a reflective means, preferably withSilver, Aluminum, a dielectric mirror or a combination of these. Peopleskilled in the art may consider other suitable reflective materialswithin the scope of this invention. The covered surfaces act as a mirrorreflecting the light towards the substrate for passing the substrate andor coupling out via the substrate into the environment. In thisembodiment, the light is reflected directly at the rear surface of theoutcoupling body without passing through the organic electroluminescentstack in front of the counter electrode. This has the advantage, thatlosses due to absorption can be minimized.

The reflective principle is suited due to the 3-dimensional form of theoutcoupling bodies. The improvement of optical outcoupling of the lightwaveguided within the substrate material is based on the change ofdirection of the light rays due to the reflection at the rear sides ofthe outcoupling body facing towards the counter electrode or at thecounter electrode itself. The top angle of the prismatic outcouplingbody has to be chosen such that light rays that are initially totallyreflected at the substrate/air interface are redirected towards thissubstrate/air interface under angles that allow the escape into air.

In the context of the invention the notion electroluminescent (EL) layerstack denotes all layers prepared between the substrate and counterelectrodes. In one embodiment of an EL layer stack, it comprises at lastone light emitting organic electroluminescent layer prepared between thesubstrate and the counter electrode. In other embodiments the layerstacks may comprise several layers prepared between the substrate andthe counter electrode. The several layers may be organic layers, such asone or more hole transport layers, electron blocking layers, electrontransport layers, hole blocking layers, emitter layers or a combinationof organic and non-organic layers. The non-organic layers may beadditional electrodes in case of two or more light emitting layerswithin the layer stack and/or charge injection layers. In a preferredembodiment the substrate electrode and or the counter electrode compriseat least one of the following materials: ITO, aluminum, silver, dopedZnO or an oxide layer.

In the context of the invention the notion substrate denotes a basematerial onto which the different layers of an electroluminescent deviceare deposited. Normally, the substrate is transparent and is made ofglass. Furthermore, it may be preferable that the substrate istransparent, preferably comprising at least one of the followingmaterials: silver, gold, glasses or ceramics. It may also be atransparent polymer sheets or foils with a suitable moisture and oxygenbarrier to essentially prevent moisture and/or oxygen entering theelectroluminescent device layer stack. It is also possible to usenon-transparent materials like metal foils as substrate. The substratemay comprise further layers, e.g. for optical purposes like lightout-coupling enhancement or other purposes. The substrate is usuallyflat, but it may also be shaped into any three-dimensional shape that isdesired.

In the context of the invention the notion substrate electrode denotesan electrode deposited on top of the substrate. Usually it consists oftransparent ITO (Indium-Tin Oxide) optionally with an undercoating ofSiO₂ or SiO to suppress diffusion of mobile atoms or ions from the glassinto the electrode. For a glass substrate with an ITO electrode, the ITOis usually the anode, but in special cases it can also be used as thecathode. In some cases, thin Ag or Au layers, typically with a thicknessof about 8 nm to 15 nm, are used single or in combination with ITO asthe substrate electrode. If a metal foil is used as the substrate, ittakes also the role of the substrate electrode, either anode or cathode.The notation on-top-of denoted the sequence of the listed layers. Thisnotation explicitly comprises the possibility of further layers inbetween the layer denoted as on top of each other. For example, theremight be additional optical layers to enhance the light out-couplingarranged between substrate electrode and substrate.

In the context of the invention the notion counter electrode denotes anelectrode away from the substrate. It is usually non-transparent andmade of Al or Ag layers of sufficient thickness such that the electrodeis reflecting, the thickness amounts typically 100 nm for Al and 100 nmto 200 nm for Ag. It is usually the cathode, but it can also be biasedas the anode. For top-emitting or transparent electroluminescent devicesthe counter electrode has to be transparent. Transparent counterelectrodes are made of thin Ag or Al layers with a thickness of about 5nm to 15 nm or of ITO layers deposited on top of the other previouslydeposited layers.

In the context of the invention an electroluminescent device with acombination of a transparent substrate, a transparent substrateelectrode and a non-transparent counter electrode, which is usuallyreflective, emitting the light through the substrate is called“bottom-emitting”. In case of electroluminescent device comprisingfurther electrodes, in certain embodiments both substrate and counterelectrodes could be either both anodes or both cathodes, when the innerelectrodes are driven as cathodes or anodes. Furthermore, in the contextof the invention an electroluminescent device with a combination of anon-transparent substrate electrode and a transparent counter electrode,emitting the light through the counter electrode is called“top-emitting”.

In the context of the invention the notion transparentelectroluminescent device denotes an electroluminescent device, wherethe substrate, the substrate electrode, the counter electrode and theencapsulation means are transparent. Here the electroluminescent deviceis both, bottom and top-emitting. In the context of the invention alayer, substrate or electrode is called transparent if the transmissionof light in the visible range is more than 50%; the rest being absorbedor reflected. Furthermore, in the context of the invention a layer,substrate or electrode is called semi-transparent if the transmission oflight in the visible range is between 10% and 50%; the rest beingabsorbed or reflected. In addition, in the context of the inventionlight is called visible light, when it possesses a wavelength between450 nm and 650 nm. In the context of the invention light is calledartificial light, when it is emitted by the organic electroluminescentlayer of the electroluminescent device.

Furthermore, in the context of the invention a layer, connector orconstruction element of an electroluminescent device is calledelectrically conducting if its electrical resistance is less than 100000Ohm. In the context of the invention passive electronic componentscomprise resistors, capacitors and inductivities. Furthermore, in thecontext of the invention active electronic components comprise diodes,transistors and all types of integrated circuits.

In the context of the invention a layer, substrate, electrode or aconstruction element of an electroluminescent device is calledreflective if light incident on its interface is returned according tothe law of reflection: the macroscopic angle of incidence equals themacroscopic angle of reflection. Also the term specular reflection isused in this case. Furthermore, in the context of the invention a layer,substrate, electrode or a construction element of an electroluminescentdevice is called scattering if light incident on it is not returnedaccording to the law of reflection: macroscopic angle of incidence isnot equal to the macroscopic angle of the returned light. There is alsoa distribution of angles for the returned light. Instead of scattering,the term diffuse reflection is also used.

In a preferred embodiment the glue is anhydrous and/or water free. Inthe context of the invention, the notion water free and/or anhydrousdescribes the fact, that no degradation due to water content during theaverage lifetime of an electroluminescent device can be observed by thenaked eye. A visible degradation of the organic electroluminescent layerdue to water diffusing into the layer stack can take the form of growingblack spots or shrinkage of the emissive region from the edges. Thenotion water free and/or anhydrous not only depends on the conductiveglue itself but also on the amount of water, which can be absorbed bythe organic electroluminescent layer without damaging it.

In a further preferred embodiment the electroluminescent device maycomprise moisture and/or oxygen barriers. In the context of theinvention layers prevention harmful diffusion of moisture and/or oxygeninto the layer stack are called moisture and/or oxygen barriers.Diffusion is denoted as harmful if a significant life-time reduction ofthe emitted light can be observed. Standard OLED devices according tostate of the art achieve shelf life times in the order of 100.000 hoursor more. A significant reduction denotes a reduced life-time of about afactor of 2 or more.

The optical transparent outcoupling bodies may be made of glass,plastics or any other optically transparent materials and may feature alongitudinal extension with a cross section, which can be triangular,prismatic, parabolic, semicircular or e.g. elliptic, whereas the opticaltransparent outcoupling body preferably is manufactured by an injectionmolding process. The outcoupling body forms a smooth, even transitionfrom the surface of the substrate electrode to the upper side of theoutcoupling body, aided by the glue used for attaching the outcouplingelements to the substrate electrode.

In its preferred embodiment, a plurality of optical transparentoutcoupling bodies is arranged on top of the substrate electrode withintermediate spaces between the optical transparent outcoupling bodiesforming a grid structure, which is preferably performed as a rectangulargrid, a hexagonal grid or an irregular grid. In the preferredembodiment, the outcoupling bodies form a symmetrical array, whereas thearray preferably is a hexagonal array. The arrangement of saidoutcoupling bodies may be extended across the entire emitting field ofthe electroluminescent device.

Advantageously, the optical transparent outcoupling body combined withthe glue for gluing the outcoupling bodies on the surface of thesubstrate electrode and in particular the grid, formed of a plurality ofoutcoupling bodies, forms a protective means. In another preferredembodiment, the glue features electrically non-conductive glue.

In a preferred embodiment the glue at least partly covers the surface ofthe optical transparent outcoupling body facing towards theelectroluminescent layer stack to prevent an emergence of a shadowingedge on the substrate electrode. This provides contiguous layers on topof the optical transparent outcoupling bodies avoiding the risk ofshorts due to layer defects around the optical transparent outcouplingbodies. Furthermore a smooth structure prevents any enhancement of theelectrical field, when voltage is applied between said two electrodes.

According to another embodiment the electroluminescent device comprisesat least one electrical contact means on top of at least one opticaltransparent outcoupling body for electrically contacting the counterelectrode to an electrical power source, whereas the electricalnon-conductive protective means is arranged at least fully covering thearea below the contact means. Said electrical contact means preferablyfeatures electrical conductive glue. This leads to the advantage that athree-dimensional contact schema with a minimum risk of shorts isprovided. The contact means has to be applied fully above the opticaltransparent outcoupling body in order to avoid any risk of shortsbetween the counter and substrate electrodes.

Usually, conductive glue consists of organic glue with conductive fillerin the form of conductive flakes or particles. During the setting of theglue, the glue may display certain shrinkage, which forces some of thefiller particles into the underlying layers, creating shorts between thesubstrate electrode and the counter electrode. To prevent this, it isadvantageous to use a protective means that is non-conductive and isbetween the substrate electrode and the counter electrode.

Therefore, all known conductive glues can be used for contacting thecounter electrode to an electrical source. The protective means has tocover the full area where the contact means is applied to the counterelectrode, since this might be the source of shorts, but it could alsobe larger than the area of the contact means. To prevent a directcontact between the counter electrode and the substrate electrode, it ispreferable that the protective means has a thickness and/or a hardness,which assures that the contact means cannot get into electrical contactwith the substrate electrode. To achieve this object, in a preferredembodiment the protective means may comprise a non-conductive glue andthe non-conductive, transparent optical outcoupling body. Usually, theoptical outcoupling body is thick and hard enough to achieve the desiredprotection. People skilled in the art may choose other electricalnon-conductive materials within the scope of the present invention.

A further advantage achieved by the usage of conductive glue as acontact means is, that a substrate with only one contiguous electrodecan be used, which serves as a substrate electrode for theelectroluminescent device. In known OLEDs, the electrode on thesubstrate is at least structured into two electrical separate regions:one serving as the substrate electrode and the other one connected tothe counter electrode. Thus, both the substrate and the counterelectrode are led in one plane to the rim of the substrate, where theycan be contacted by standard means. The disadvantage of this2-dimensional contacting scheme is that the substrate electrode as wellas the counter electrode have to share the periphery of the OLED forcontacting, so that the electrode on the substrate needs to be dividedinto at least two disjoint regions, namely the substrate electrode and asecond electrode to be contacted with the counter electrode, to avoidshorting the device. The disclosed 3-dimensional contacting eliminatesthis serious disadvantage of the 2-dimensional contacting.

To prevent a direct contact between the counter electrode and thesubstrate electrode, it is preferable that the protective means has athickness and/or a hardness, which assures that the contact means cannotget into electrical contact with the substrate electrode. To achievethis object, in a preferred embodiment the protective means may comprisenon-conductive glue and the non-conductive, transparent opticaloutcoupling body. Usually, the optical outcoupling body is thick andhard enough to achieve the desired protection. People skilled in the artmay choose other electrical non-conductive materials within the scope ofthe present invention.

The electroluminescent device comprises an encapsulation means, which isarranged for encapsulating at least said electroluminescent layer stack,whereas the electrical contact means is preferably arranged in betweensaid encapsulation means and the counter electrode for electricallycontacting the counter electrode to the encapsulation means. Theencapsulation means may also encapsulate the whole stack of layers ofthe electroluminescent device or just a plurality of layers, forming apart of the whole stack of layers. Preferably, the encapsulation meansis provided as a gas-tight element, covering at least the organicelectroluminescent layer and the counter electrode. By using a gas-tightencapsulation means, it is prevented that environmental factors likewater or oxygen damage the encapsulated layers. The encapsulation meansmay form a gas-tight lid. This lid may be formed of glass or metal. Itis also possible to form the encapsulation means by one or a pluralityof layers supplied to the electroluminescent device or just parts of it.The layers may comprise silicone, silicone oxide, silicone nitride,aluminum oxide or silicone oxynitride. All the named encapsulation meansprevent mechanical and/or environmental factors from affecting the layerstack of the electroluminescent device adversely. As an example, theencapsulation means can be made of metals, glasses, ceramics orcombinations of these. It is attached to the substrate by conductive ornon-conductive glue, melted glass frit or metal solder. Therefore, itmay also provide mechanical stability for the electroluminescent device,whereas at least parts of the applied glue between the layers and theencapsulation means is electrical conducting for contacting the counterelectrode.

According to yet another embodiment of the present invention comprisesat least one electrical shunt means, which can be applied to thesubstrate electrode to minimize the voltage drops within the lateralextension of the substrate electrode, wherein the electrical shunt meansis arranged on the surface of the substrate electrode and whereas saidoutcoupling body covers the electrical shunt means in a way, that theelectrical shunt means is arranged between said substrate electrode andsaid optical outcoupling body. Thus, the optical outcoupling body can beglued to the substrate electrode by optical transparent glue asdescribed above, featuring a high index of refraction. The electricalshunt means can be at least one element of a group of a wire, a metallicstripe or a metallic foil. Furthermore said electrical shunt means isfixed to the substrate electrode by electrically conductive glue,limited to parts of the area of the electrical shunt means.

Preferably, the electrical shunt means is electrically connected atleast at the end points and maybe at some points in the middle. As aresult, a glue-in-glue-arrangement can be applied for electricallycontacting the electrical shunt means to the substrate electrode by theuse of electrically conductive glue, but the remaining area between theoptical outcoupling body and the substrate electrode is filled withelectrical non-conductive glue featuring a high index of refraction andtransparency. In order to arrange said electrical shunt means in asandwich-like manner between the optical outcoupling body and thesurface of the substrate electrode, said optical outcoupling body mayhave a kind of recess in the bottom surface for receiving said wire,metallic stripe or foil.

The present invention is also directed to a method for manufacturing anelectroluminescent device with an increased outcoupling of light,whereas the method comprises at least the steps of providing at leastone optical transparent outcoupling body on top of the substrateelectrode and a subsequent application of the electroluminescent layerstack and the counter electrode both on the optical transparentoutcoupling body and on the surface of the substrate electrode.Moreover, the method is embodied in at least one optical transparentoutcoupling body, which is glued on top of the substrate electrode bytransparent glue. Advantageously the glue is applied at least partly ontop of the surface of the optical transparent outcoupling body facingtowards the electroluminescent layer stack to prevent an emergence of ashadowing edge on the substrate electrode.

In the preferred embodiment, the glue is applied at least partly on topof the surface of the optical transparent outcoupling body facingtowards the electroluminescent layer stack to prevent an emergence of ashadowing edge on the substrate. The application of the glue, preferablyof the non-conductive glue, forms a smooth and flat transition betweenthe surface of the substrate electrode and the upper sides of theoutcoupling body. The application of the glue leads to an improveddeposition process of said layers on top of the substrate electrode witha smooth transition into the surface of the outcoupling body, wherecontiguous layers of the electroluminescent layer stack and the counterelectrode can be prepared. In contrast to that, shadowing edges wouldlead to a lesser amount of material or no amount of material depositedaround the shadowing edges. By applying the method according to theinvention using non-conductive glue, a local enhancement of theelectrical fields in the area of the outcoupling body can be avoided.

The aforementioned electroluminescent device and/or the method, as wellas claimed components and the components to be used in accordance withthe invention in the described embodiments are not subject to anyspecial exceptions with respect to size, shape or the materialselection. Technical concepts such as the selection criteria are knownin the pertinent field can be applied without limitations. Additionaldetails, characteristics and advantages of the object of the presentinvention are disclosed in the subclaims and the following descriptionof the respective figures, which are an exemplary fashion only, showinga plurality of preferred embodiments of the electroluminescent deviceaccording to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Further embodiments of the invention will be described with respect tothe following figures, which show:

FIG. 1 an embodiment of an electroluminescent device according to theinvention with outcoupling bodies applied on the substrate electrodewith a first reflection principle,

FIG. 2 an embodiment of an electroluminescent device with outcouplingbodies applied on the substrate electrode with a second reflectionprinciple,

FIG. 3 an embodiment of an electroluminescent device with outcouplingbodies and with electrical shunt means,

FIG. 4 an embodiment of an electroluminescent device with an outcouplingbody and an electrical contact means for electrical contacting thecounter electrode, shown in a detailed cross section and

FIG. 5 a side view and a cross sectional view of an embodiment of theelectroluminescent device comprising an optical outcoupling body and ashunt means.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In FIG. 1 an electroluminescent device 10 according to an embodiment ofthe invention is shown. The electroluminescent device 10 comprises asubstrate electrode 20, a counter electrode 30 and an organicelectroluminescent layer 50 representing the electroluminescent layerstack in this and the following embodiments. The organicelectroluminescent layer 50 is arranged between the substrate electrode20 and the counter electrode 30 forming said layer stack. These layersare arranged on a substrate 40, forming the carrier material of theelectroluminescent device 10. In the shown embodiment the substrateelectrode 20 is formed by an approximately 100 nm thick layer of ITO,which is a transparent and conductive material. Onto this substrateelectrode 20 the organic electroluminescent layer 50 is deposited. If avoltage is applied between the substrate electrode 20 and the counterelectrode 30 some of the organic molecules within the organicelectroluminescent layer 50 are exited, resulting in the emission ofartificial light, which is emitted by the electroluminescent layer 50.The counter electrode 30 is formed by a layer of aluminum, working as amirror reflecting the artificial light through the substrate electrode20 and the substrate 40. To emit light into the surrounding thesubstrate 40 in this embodiment is made of glass. Thus, theelectroluminescent device 10 is a bottom emitting OLED. Theelectroluminescent device 10 shown in the following figures as well asthe components and the components used in accordance with the inventionare not shown true to their scale. Especially the thickness of theelectrodes 20 and 30, the organic electroluminescent layer 50 and thesubstrate 40 are representing a not true scale. All figures just serveto clarify the invention.

As shown in detail, the electroluminescent device 10 comprises opticaltransparent outcoupling bodies 71. The optical transparent outcouplingbodies 71 have a specific spatial geometry, a triangular or prismaticshape, representing only one embodiment of a plurality of differentpossible shapes. The optical transparent outcoupling bodies 71 lead toan improved outcoupling of light, generated by the organicelectroluminescent layer 50, exemplarily shown by an organicelectroluminescent point 50′. The optical transparent outcoupling bodies71 are made of an optical transparent material having an index ofrefraction, which is nearly equal to or higher than the index ofrefraction of the substrate 40 of the electroluminescent device 10. Thelight, emitted by the organic electroluminescent point 50′ entering theoptical outcoupling body 71, is reflected at the upper side of theoutcoupling body 71 towards the substrate electrode 20 again. Thereflected light now has a direction, which allows it to pass the bottomsurface of the substrate 40. By means of said outcoupling bodies 71 theportion of light emitted by the electroluminescent device 10 is thusincreased. In order to ensure the reflection of light in the uppersurface of the optical outcoupling bodies 71, the optical outcouplingbodies 71 feature reflective means 72.

As shown in the depiction, the organic electroluminescent layer 50,representing the electroluminescent layer stack and the counterelectrode 30 is applied on the surface of the substrate electrode 20 aswell as on the upper side of the optical transparent outcoupling bodies71. The application of the organic electroluminescent layer 50 and thecounter electrode 30 on top of said surfaces is based on a vacuumdeposition process as known to a person skilled in the art. The glue 70prevents a current flow between the substrate electrode 20 and thereflective means 72, which can be formed by metallic cover elements or asurface layer, each may feature electrical conductivity.

FIG. 2 shows the embodiment where the reflection of light entering theoptical outcoupling bodies 71 happens on the counter electrode 30 behindthe outcoupling bodies. The light enters into the optical outcouplingbodies 71 and leaves the optical outcoupling bodies 71 at the upper sideagain, propagating towards the counter electrode 30 for reflecting onthe inner reflective surface 73 of the counter electrode 30. As shown,the optical outcoupling bodies 71 are attached to the substrateelectrode 20 by the use of transparent glue 70. The glue 70 covers thesurface of the substrate electrode 20 below the arrangement of theoutcoupling body 71 and extends into the neighboring areas of theoutcoupling bodies 71. The presence of glue 70 in the transition regionbetween the substrate surface and the upper side of the outcouplingbodies 71 leads to a flat, smooth transition between the outcouplingbody and the substrate electrode. Due to the presence of said glue theshadowing effect is avoided, and the deposition of the layer systemcomprising at least the organic electroluminescent layer 50 and thecounter electrode 30, respectively, can be performed with an improvedreliability.

FIG. 3 shows another embodiment of the electroluminescent device 10according to the present invention illustrating optical outcouplingbodies 71, whereas the optical outcoupling bodies 71 cover electricalshunt means 122, applied on the surface of the substrate electrode 20.Thus, this arrangement of electrical shunt means 122 is performedsandwich-like in between said substrate electrode 20 and said opticaloutcoupling bodies 71. Moreover, the optical outcoupling bodies 71combined with electrical non-conductive glue 70 forms a protective means70, preventing shorts between the electrical shunt means 122 and thecounter electrode 30.

FIG. 4 shows the arrangement of an electroluminescent device 10comprising a contact means 60. The electroluminescent device 10 maycomprise at least one or a plurality of the depicted contact means 60,arranged for electrically contacting the counter electrode 30 to anelectrical power source. The contact means 60 is therefore part of thepath leading from the counter electrode 30 to the electrical source. Inthe prior art contact posts are used as contact means 60, which areapplied to the counter electrode 30. Such contact posts have thedisadvantage that they are mechanically applied to the counter electrode30 and often lead to shorts between the counter electrode 30 and thesubstrate electrode 20. To overcome this disadvantage, the inventiondiscloses that the contact means 60 is conductive glue, applied to thecounter electrode 30.

The contact means 60 can be formed by electrical conductive glue,arranged in direct electrical contact with the counter electrode 30 aswell as the shown encapsulation means 90. Therefore, it is easy toelectrically connect the counter electrode 30 to an electrical powersource via said encapsulation means 90. The user just has to apply anelectrical conductive means to the encapsulation means 90. Theconductive glue between the encapsulation means 90 and the counterelectrode 30 then leads the electrical current to the counter electrode30.

When conductive glue is used to form the electrical contact means 60, apreferred embodiment of the disclosed electroluminescent device 10comprises a protective means 70, which is formed by the glue 70 and theoptical transparent outcoupling body 71. As shown, the electricalnon-conductive protective means 70 is arranged at least fully coveringthe area below the contact means 60. The protective means 70 is arrangedon the substrate electrode 20, and an electrical shunt means 122 isarranged sandwich-like between the protective means 70, embodied as theoptical transparent outcoupling body 71 and the surface of the substrateelectrode 20 for shunting the substrate electrode 20. This arrangementprotects the area below the contact means 60 and can also form anoptical outcoupling system as well as a shunting system. Thus, thisarrangement using the protective means 70 satisfying three objectives,namely fully covering the shunt means 122 and fully covering the areabelow the electrical contact means 60, requiring electricalnon-conductive glue forming the protective means 70. Furthermore, theoptical outcoupling of the light emitted by the organicelectroluminescent layer 50 is improved.

FIG. 5 shows another embodiment of the electroluminescent device 10 in aside view and a cross section. As shown, the electrical shunt means 122can be lead out of the arrangement comprising the optical transparentoutcoupling body 71 and the layer system comprising at least the organicelectroluminescent layer 50 and the counter electrode 30. The electricalshunt means 122 is applied on the surface of the substrate electrode 20and extends in lateral direction beside the arrangement of said layersand in particular the arrangement of the optical transparent outcouplingbody 71. The counter electrode 30 is contacted by the connection means93, as shown only in exemplary fashion. The electrical shunt means 122can be contacted to the substrate electrode 20 via contact means 74 atboth ends and at a few points along its length, in order to equalize thevoltage across the emitting field of the organic electroluminescentdevice 10. In particular, by applying the electrical shunt means 122,the electrical voltage at the centre of the electroluminescent device 10is aligned to the electrical voltage in the outer regions of theemitting field of the electroluminescent device 10 during operation.

The described embodiments comprise as an example an organicelectroluminescent layer 50 within the layer stack. In alternativeembodiments within the scope of this invention, the electroluminescentlayer stack may comprise layer additional to organic electroluminescentlayer 50 such as hole transparent layers, hole blocking layers, electrontransport layer, electron blocking layers, charge injection layers,further conducting layers, etc.

1. An electroluminescent device comprising: a substrate; a substrateelectrode disposed on the substrate; a counter electrode; at least oneorganic electroluminescent layer disposed between the substrateelectrode and the counter electrode; and at least one opticallytransparent body disposed on the substrate electrode, wherein theoptically transparent body is arranged to increase the outcoupling oflight generated by the at least one organic electroluminescent layer,wherein the at least one organic electroluminescent layer covers atleast a portion of the optically transparent body; wherein a firstsurface of the counter electrode that faces the substrate is coveredwith a reflecting material.
 2. The electroluminescent device accordingto claim 1, wherein the reflecting material is selected from the groupconsisting of silver, aluminum, and a dielectric mirror.
 3. Theelectroluminescent device according to claim 1, wherein the reflectingmaterial comprises silver.
 4. The electroluminescent device according toclaim 1, wherein the optically transparent body comprises an index ofrefraction, the index of refraction at least matching the index ofrefraction of the substrate.
 5. The electroluminescent device accordingto claim 1, wherein the optically transparent body comprises alongitudinal extension with a cross section, wherein the cross sectionis selected from the group consisting of rectangular, triangular,prismatic, parabolic, semi-circular and elliptic.
 6. Theelectroluminescent device according to claim 1, wherein the reflectingmaterial is disposed on a second surface of the optically transparentbody, the second surface facing towards the organic electroluminescentlayer.
 7. The electroluminescent device according to claim 1, whereinthe at least one optically transparent body is fastened to the substrateelectrode by a glue.
 8. The electroluminescent device according to claim7, wherein the glue is transparent to the light emitted from theelectroluminescent device, wherein the glue has an index of refraction,wherein the index of refraction at least matches the index of refractionof the substrate.
 9. The electroluminescent device according to claim 7,wherein the glue is electrically non-conductive, wherein the glue isarranged to prevent electrical contact between the substrate electrodeand the counter electrode.
 10. The electroluminescent device accordingto claim 7, wherein the optically transparent body has a third surfacefacing towards the organic electroluminescent layer, wherein the glue atleast partly covers the third surface, wherein the glue is arranged toprevent an emergence of a shadowing edge on the substrate electrode. 11.The electroluminescent device according to claim 7, wherein theelectroluminescent device comprises at least one electrical contact ontop of the at least one optically transparent body, wherein the at leastone electrical contact is arranged to electrically connect the counterelectrode to an electrical power source.
 12. The electroluminescentdevice according to claim 11, wherein an encapsulation is arranged toencapsulate at least the at least one organic electroluminescent layer,wherein the electrical contact is disposed between the encapsulation andthe counter electrode, wherein the counter electrode is arranged toelectrically connect the counter electrode to the encapsulation.
 13. Theelectroluminescent device according to claim 1, wherein at least oneelectrical shunt is disposed on the substrate electrode, wherein thesubstrate electrode is arranged to align an electrical potential withinthe lateral extension of the substrate electrode, wherein the electricalshunt is disposed between the substrate electrode and the opticallytransparent body.
 14. The electroluminescent device according to claim1, further comprising a plurality of optically transparent bodies,wherein the plurality of optically transparent bodies are disposed ontop of the substrate electrode, wherein the plurality of opticallytransparent bodies are arranged with intermediate spaces between theplurality of optically transparent bodies.
 15. The electroluminescentdevice according to claim 14, wherein the plurality of opticallytransparent bodies form a grid structure.
 16. A method of manufacturingan electroluminescent device, the method comprising: providing asubstrate; disposing a substrate electrode on the substrate; providing acounter electrode; disposing at least one organic electroluminescentlayer between the substrate electrode and the counter electrode; anddisposing at least one optically transparent body on of the substrateelectrode, wherein the organic electroluminescent layer covers at leasta portion of the optically transparent body, wherein a first surface ofthe counter electrode that faces the substrate is covered with areflecting material.
 17. The electroluminescent device according toclaim 16, wherein the reflecting material comprises silver.
 18. Themethod according to claim 16, wherein the at least one opticallytransparent body is fastened to the substrate electrode by a glue. 19.The method according to claim 16, wherein the at least one opticallytransparent body has a second surface facing towards the organicelectroluminescent layer, wherein the glue is applied at least a portionof the second surface, wherein the organic electroluminescent layer isarranged to prevent an emergence of a shadowing edge on the substrateelectrode.
 20. An electroluminescent device, comprising: a substrate; asubstrate electrode adjacent to the substrate; a counter electrode; andan at least one electroluminescent layer, wherein the electroluminescentlayer is disposed between the substrate electrode and the counterelectrode, wherein a surface of the counter electrode that faces thesubstrate is covered with a reflecting material, wherein at least oneoptically transparent body is affixed to the substrate electrode by anelectrically non-conductive glue, wherein the at least one opticallytransparent body is arranged to increase the outcoupling of lightgenerated by the at least one organic electroluminescent layer, whereinthe organic electroluminescent layer surrounds at least a portion of theat least one optically transparent body, wherein the at least oneelectrical contact is disposed on top of at least one opticaltransparent body.